Development of photoselective covers

(image: YBM-1 (left) and YBM-10 (right) experimental chambers. As the dye concentration increased light transmission decreased. Irradiance indside each chamber was adjusted to be the same with shade cloth or cheesecloth. Chambers are approximately 1m x 1m x 1m.) Mitsui
Chemicals, Inc. identified two pigments that absorb far-red light from
the natural spectrum and that are stable in polyethylene films or rigid
plastic panels. Initial trials focused on identifying a suitable dye and
dye concentration that effectively filters out far-red light from sunlight
and reduces plant height while minimizing the reduction in light transmission.
Mitsui Chemicals, Inc produced rigid plastic panels containing five dye
concentrations from each dye. (Figure
2. Plant response inside YMB-1 (left column) or YMB-10 (right column)
chambers with varying dye concentrations. Within a picture, from left
to right, are plants grown in control, #85, #75, #65, and #55 chamber.
Within a column, pepper, watermelon, chrysanthemum, tomato, and petunia
are shown from top to bottom.)These were identified as control, YBM-1/YBM-10
#85, YBM-1/YBM-10 #75, YMB-1/YBM-10 #65, and YBM-1/YBM-10 #55. The number
followed by the YBM indicates the code of the dye. As the dye concentration
in the panels increased, the absorption of far-red light increased but
the light transmission decreased. The number followed by YBM-1 or YBM-10
indicates the percentage light transmission through each panel. Growth
chambers (1 m x 0.8 m x 0.8 m) were built with each of these
materials and growth of bell pepper, tomato, petunia, and watermelon seedlings
and chrysanthemums cuttings were evaluated inside each of the chambers.
All chambers were kept inside a greenhouse and the amount of light inside
each chamber was adjusted with neutral density filters (cheesecloth or
shade cloth) to be the same among all chambers.

Both types of far-red light
absorbing photoselective filters reduced height of all species tested in
preliminary trails but the magnitude of height reduction varied with the
species. (Table 2 and
Figure
2). In general, watermelon seedlings showed the greatest height
reduction followed by bell peppers, tomato, and chrysanthemum. Number of
leaves was not affected, indicating that height reductions were caused
by shorter internodes. The height reduction increased as the dye concentration
in the panels increased but total shoot dry weight was reduced because
of the severe light reduction as the dye concentration increased. Therefore,
a dye concentration that gives a light transmission of 75% was selected
for photoselective film production and further experimentation.

Table 2. Effect of dye concentrations in YBM-1 and YBM-10 photoselective
chambers on height of chrysanthemum, watermelon, bell pepper, and tomato
plants. The number followed by the film indicates the percent light transmission
through the panels. Percentage height reductions compared to control plants
are given in parentheses.

Plant height (cm)

Material

Chrysanthemum

Watermelon

Bell pepper

Tomato

Control

29.7

28.4

22.1

-

YBM-1 #85

26.6 (-10)

21.7 (-24)

17.2 (-22)

-

YBM-1 #75

23.7 (-20)

14.6 (-49)

13.9 (?37)

-

YBM-1 #65

20.9 (-30)

14.5 (-49)

13.9 (-37)

-

YBM-1 #55

21.8 (-27)

14.9 (-48)

12.0 (-46)

-

Control

30.2

52.3

14.5

35.0

YBM-10 #85

31.0 (+3)

38.9 (-26)

11.2 (-23)

32.5 (-7)

YBM-10 #75

25.9 (-14)

38.1 (-27)

10.0 (-31)

23.2 (-34)

YBM-10 #65

26.2 (-13)

35.0 (-33)

9.9 (-31)

23.4 (-33)

YBM-10 #55

27.0 (-11)

33.2 (-37)

9.6 (-34)

23.7 (-32)

(image: Response bell pepper (top), tomato (center), and cucumber (bottom) seedlings to photoselective films.) Based on initial findings,
photoselective greenhouse films with red and far-red light absorbing films
(SXE-4 and YXE-10 films, respectively) were produced with a dye concentration
that results in a 75% light transmission (
light spectrum (image) of two types of films). Growth of several vegetable
transplants and ornamental bedding plants was evaluated inside
growth
chambers covered with these films. The results are summarized
in Table 3. Plants produced under the far-red light absorbing film were,
in general, shorter (except snapdragon and miniature roses) than the control
plants while plants produced under the red light absorbing film had similar
or increased height compared to the control plants. The magnitude of height
reduction varied with the species and cultivar.

We also evaluated flowering
of selected ornamental crops inside the chambers under natural short day
conditions. Flowering of miniature rose plants was not affected (Table
3). Flowering of cosmos, zinnia, and chrysanthemum (short day plants) was
slightly delayed (by 1-2 days) under the far-red light absorbing film.
Photoselective films had the greatest influence on flowering of snapdragon
and petunia (long-day plants). Flowering of these species was delayed by
7-13 days under the far-red light absorbing films. Red light absorbing
film did not significantly affect flowering of these species tested.

Table 3. Influence of red and far-red light absorbing plastic
films (SXE-4 and YXE-10, respectively) on plant height and flower development
(days to anthesis, DA) under natural short days of selected crops. Control
is a clear polyethylene film.

Control film

SXE-4 film

YXE-10 film

Crop

Height
(cm)

DA
(days)

Height
(cm)

DA
(days)

Height
(cm)

DA
(days)

Vegetable crops

Cucumber
‘Sweet Success’

17.3 b

-

19.8 a

-

8.6 c

-

Tomato‘Mountain
Pride’

15.0 a

-

15.8 a

-

11.2 b

-

Bell
pepper ‘Capistrano’

11.1 a

-

11.4 a

-

8.4 b

-

Ornamental crops

Snapdragon

'Ribbon White’

48.3 b

63 b

53.8 a

61 b

48.9 b

70 a

‘Tahiti Red’

25.5 a

51 b

24.7 ab

50 b

23.0 b

59 a

Florida pink

23.6 b

26 a

27.2 a

27 a

22.5 b

25 a

Florida blue

31.2 a

30 a

30.4 a

28 a

27.9 b

31 a

Florida sky blue

26.7 ab

30 a

28.1 a

30 a

23.4 b

32 a

Petunia

‘Supercascade Burgandy’

-

53 b

-

54 b

-

66 a

Zinnia

‘Pumila Mix’

24.5 b

33 ab

28.4 a

32 b

18.8 c

35 a

‘Cherry Ruffles’

38.0 a

35 c

40.9 a

36 b

30.4 b

37 a

Cosmos

‘Sonata White’

37.3 a

26 a

38.1 a

27 a

33.5 b

27 a

Miniature rose

‘Cherry Cupido’

28.8 a

46 a

29.2 a

46 a

27.2 a

46 a

Chrysanthemum

‘Bright Golden Anne’

32.6 b

64 a

34.6 a

65 a

28.4 c

65 a

‘Iridon’

22.6 b

59 a

25.8 a

60 a

19.8 c

62 a

‘Yellow Snowden’

50.8 a

55 a

50.4 a

57 a

40.7 b

56 a

Pachystachys
lutea

30.1 b

38 a

32.8 a

38 a

27.0 c

38 a

Strobilanthes
dyerianus

34.2 ab

-

38.9 a

-

30.2 b

Response of Petunia and Snapdragon (long day plants) to photoselective films.